The present invention relates to a collapsible lens barrel and an image pickup apparatus.
Some lens barrels incorporated in image pickup apparatuses such as digital still cameras, digital video cameras, etc. have a cam ring with a cam groove defined in an inner circumferential surface thereof and a lens holder frame which is nonrotatably, but axially movably held radially in the cam ring and which holds a lens assembly. The lens holder frame has a cam pin engaging in the cam groove such that the lens holder frame moves axially when the cam ring rotates about its own axis. For details, see Japanese Patent Laid-open No. 2002-267917, for example.
One such lens barrel is illustrated in FIG. 30 of the accompanying drawings. As shown in FIG. 30, the lens barrel has a linear guide ring 3 interposed between the outer circumferential surface of a lens holder frame 1 and the inner circumferential surface of a cam ring 2.
The linear guide ring 3 is nonrotatably mounted on the lens barrel 1 and has axially linear guide grooves 3A defined therein. Cam pins 1A of the lens holder frame 1 extend through the guide grooves 3A and engage in cam grooves 2A defined in the cam ring 2. The lens holder frame 1 is nonrotatably, but axially movably held radially in the cam ring 2.
With the lens barrel in related art, however, since the linear guide ring 3 is interposed between the outer circumferential surface of the lens holder frame 1 and the inner circumferential surface of the cam ring 2, it poses limitations on efforts to reduce the diameter of the lens barrel and hence size of the lens barrel.
If the lens barrel has two lens holder frames 1 (only one lens holder frame 1 is shown in FIG. 30), then the cam grooves 2A in the cam ring 2 which are engaged by the cam pins 1A, 1B of the lens holder frames 1 extend continuously circumferentially at least fully around the cam ring 2, and the cam pins 1A, 1B are guided at different positions in the guide grooves 3A in the linear guide ring 3.
The lens holder frames 1 are assembled into the cam ring 2 with the linear guide ring 3 interposed therebetween, as follows.
First, the linear guide ring 3 is inserted into the cam ring 2, and then turned to align the guide grooves 3A with open ends 2B of the cam grooves 2A in the cam ring 2. Then, the cam pins 1A of one of the lens holder frames 1 are inserted into the open ends 2B and caused to engage in the cam grooves 2A.
Then, the cam ring 2 is rotated by one revolution to move the one of the lens holder frames 1 axially.
Thereafter, the linear guide ring 3 is turned to align the guide grooves 3A with the open ends 2B of the cam ring 2. Then, the cam pins 1B of the other lens holder frame 1 are inserted into the open ends 2B and caused to engage in the cam grooves 2A.
Then, the cam ring 2 is rotated to move the other lens holder frame 1 axially.
The assembling process is complex because the guide grooves 3A of the linear guide ring 3 need to be aligned with the open ends 2B of the cam grooves 2A twice and the linear guide ring 3 needs to be rotated by one revolution.